The invention relates to a method for heating an aluminum electroplating bath of aprotic electrolyte solvent to a prescribed working temperature and keeping the working temperature constant during the aluminum electroplating process.
In installations for the electrodepositing or electroplating of aluminum, there is provided an electroplating tank or trough which contains a heated aprotic, aluminum-organic electrolyte kept under oxygen-free and water-free conditions. The electrolyte must be heated to an operating temperature of over 80.degree. C. in order to promote useful and substantially economic aluminum precipitations on pieces to be plated. The warming and continued heating of such electrolyte presents difficulties since aluminum electrolytic baths can react with the oxygen and the moisture of air causing a considerable reduction in the conductivity and life of the electrolyte and, furthermore, are also highly flammable. Accordingly, direct heating of the electrolyte is not practical, but rather is conventionally undertaken by indirect heating.
Typically, aluminization electrolyte is heated in the electroplating tank by means of an oil jacket which surrounds the tank and in which suitable heating elements are situated. This arrangement is shown, for example, in U.S. Pat. Nos. 4,053,383 and 4,176,034 and the German Offenlegungsschrift No. 2537285. It is also known to heat aluminization electrolyte by a continuous pumping of electrolyte out of the electroplating tank through a heat exchanger and then back into the tank. These known arrangements for heating aluminization electrolyte, however, have drawbacks in that there may be relatively high thermal losses, higher manufacturing costs such as for thermal installation and when a heating jacket or pipe lines and pumps are required, and they necessitate a suitably complicated and expensive temperature control mechanism.
The present invention is directed to a simplified method for heating an aluminum electroplating bath of aprotic electrolyte which requires little outlay and can be easily set to practically any prescribed working temperature.